To Defence counsel Richard Rampton
QC and to the High Court it seemed inconceivable that there
was any explanation, other than homicidal, for the presence
of a peephole with a protective grill in the gastight doors
to be installed in the underground Krema II
building.

.

Website
illustration

Above:
An advertisement from the wartime German civil defense
manual, for standard air raid shelter doors and shutters
-- the doors have a peephole and protective
grill.

Right
(click image to enlarge) -- and instructions (below):
From page 256 of Neufert, the standard Third Reich
architectural manual demonstrably used at Auschwitz and
elsewhere: diagrams of air raid shelters always included
outward opening gastight doors with peepholes.